Dense rubbery compositions



Patented Apr. 4, 1950 2,502,949 DENSE RUBBERY COMPOSITIONS Richard M. Hewlett, Roselle, and Raymond G. Newberg, Cranford, N. 3., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application October 5, 1945,

Serial No. 620,632

This invention relates to an improved method for incorporating dense fillers in rubbery compositions and forming improved products. More particularly, this invention relates to incorporation of fusible metallic substances, as dense fillers, in a fused condition into a rubbery compound at a processing temperature.

High density rubber stocks have at times been made by incorporating powdered lead. The lead incorporated stocks have had Various uses as counterweights, X-ray blocking and X-ray protective materials, and others. The incorporation and dispersion of the lead was difiicult. The power consumption in milling was excessive. The stocks were difficult to mold.

The difficulties of incorporating powdered lead in a rubber stock are overcome by the method of t'm's invention, by which a metal is incorporated as a liquid or molten mass into a rubbery compound at processing temperatures.

-An object of this invention is to provide a method of incorporating a metal in fused condition into rubbery compounds at normal processing temperatures, preferably at temperatures below 300 F.

The dense metallic substance or filler may be a metal or alloy which melts or softens at the processing temperature and preferably at a temperature below 300 F. A number of alloys containing bismuth, tin, and lead are suitable. Woods alloy, which is composed of about 50% bismuth, 25% lead, 12.5% tin, and 12.5% cadmium and has a melting point of about 65.5 0., may be used.

The method is applicable for incorporating the fusible metallic fillers into stocks of natural and Synthetic rubbers. The synthetic rubbers include vulcanizable rubbery gums or resins, such as copolymers of butadiene, isoprene, or other diolefins with styrene, alpha alkyl styrenes, ring substituted alkyl styrenes, chloro-styrenes, acrylonitrile, alpha methacrylonitrile, unsaturated esters like methyl methacrylate or other copolymerizable organic compounds. It is also advantageously applicable to rubbery copolymers having relatively low unsatur-ation, such as butyl rubber copolymers.

' Butyl rubber copolymers are in general copolymers of olefins, such as isobutylene, with smaller amounts of diolefins. Methods of producing and the properties of these copolymers are described in the U. S. Patent 2,356,128, issued August 22, 1944, to Robert M. Thomas et al. The copolymerized monomers are preferably such proportio'ns'as '70 to 99 /2 parts of isobutyle'ne" with 30 to parts of dioleiin, e. g., of isoprene or butadiene. These copolymers have high chemical resistance and are in some respects extraordinary in processing and vulcanizing.

For one mode of operation, the stock is placed 3 Claims. (Cl. 260-415) on a warm mill and the melted metal is readily worked into'the polymeric material in a manner commonly used for incorporating liquid softeners. So long as the metal is kept above its melting point, mixing proceeds in a normal fashion. This condition is obtained with a stock having a suitable temperature in being processed on the warm mill.

Woods alloy or metal was compounded into typical butyl rubber stocks with substantiation of the foregoing principles. All ingredients except the metal were incorporated in the stock by following normal mixing procedure on a rubber mill. The mill temperature was then raised to 160 F. and a stick of Woods alloy was pressed against the hot back roll. The metal immediately became fluid and worked into the stock with no difficulty. The finished stock was cured satisfactorily in 60 minutes at 307 F. with no sign of bloom and a satisfactory smooth sheet was obtained. Illustrative details are given in the following table.

TABLE I Cure: 60 minutes at 307 F.

The stocks are molded with no difiiculty. For example, compounding ingredients containing preferably a delayed action accelerator may be placed in a mold without applying pressure until the stock temperature is above the melting point of the metal, e..g., above C. for Woods alloy. When the pressure is applied, the metal becomes liquid, and free flowing stock in the mold is assured.

A metal may be similarly incorporated into stocks of natural rubber and synthetic rubbers of various types, e. g., copolymers of butadiene with styrene (Buna S), copolymers of butadiene with acrylonitrile (Perbunan'), representative of other vulcanizable rubbery gums Or resins.

In compounding stocks described in the fol lowing tables, the normal compounding procedure was followed. Fillers including the Woods metal were mixed into the gum first. The stock was then removed from the mill and allowed to cool. After cooling, the accelerators, activators, and 1.5 to 4 parts of sulfur per parts of gum were added as in normal compounding.

TABLE 11 High density butyl rubber In molding stocks such as illustrated in Tables II to V, no warm-up time was necessary. The stocks were free flowing and the metal was disw h persed so that the composition was homogeneous medium Pam by t with no globules of metal detectable.

Amounts ranging from 1 or several parts to ii oiiiiit?Bff'?:t::::::::::::::::: "2 i3 300 parts of the metallic filler per 100 of Stearic Acid a g gum maybe incorporated with advantages sought 'gggg fii gf figgggggg ggf 1 and obtained, such as ease of dispersion, heavy s 1.5 4 loading without excessive hardness or stiffness, gfggggggg ammphw satisfactory molding quality, smoothness, and Cabot #9 (Easy processing channel black) 25 capability of being flexed without cracking. Spe ific Gravity t 25 C 1. 41 1.67 ease of P and Puring with com- Tensile-Modulus at 300% 940-70 1,750-Z60 positions containing conventional ingredients giggj at 30 1109043 l5 and under ordinary processing conditions was som at 307; 1,13o7o 1, 660-340 surprising. Conditions of overheating that cause 1501mmat37 F 109045 66045 deterioration of the stock were fully avoided.

Other modifications are intended to be in- TABLE III eluded within the scope of the invention as de- Hz-gh density perbumm fined in the appended claims.

We claim: 1. In the method of producing a dense rubb h Ingredients Pam yweig t bery article, the improved step which comprises adding in the molten state from 1 to 300 parts P b 26 100 10c gico33e i f@ 2 1g of an alloy of 50% bismuth, lead, 12 Mm Ci tin and 12 /2% cadmium to 100 parts of a rub- Alt B m lDi m 1 2 Pini l ar f i 1o bery copolymer of 70 to 99 of isbutylene and tii(statuessassaaasssas1: 2% 5 to 1/2% of a conjugated diolefin, thoroughly Gastex (Semi-reinforcing furnace mixing the molten alloy into the rubbery copolywtiiiihzsiiiij:::::::::::::::::3: 50 E3 30 by mastication at a temperature which is no 1 41 1 5 above the melting point of the alloy and vulgggg ggf gegggjggg 5 5 0 canizing the resulting composition at a temper- Cure: ature above the melting point of the alloy.

2. In the method of producing a dense vul- 35023058 canized rubbery article, the step which comprises adding in the molten state from 1 to 300 parts of an alloy of 50% bismuth, 25% lead, 12 tin and 12 cadmium and 1.5 to 4 parts of h Hm denszty S sulfur to 100 parts of a rubbery copolymer of 70 40 to 99 /2% of isobutylene and 30 to /z% of isomgredems Parts by Weight prene, thoroughly mixing the molten alloy into the rubbery copolymer by mastication at a temg 28 perature which is above the melting point of the grease Ale/ltd i5 2 alloy, and vulcanizing the resulting composition 11%;: Teii r i e thi i flfiufi i fiil' at a temperature above the melting point of the osnlfide) c- 1. 2 alloy. l iififiii fffi ii .ffffiiiiiii::2 3.0 E In the method of producing a dense Celite (Hylratied ilhmorriillliousfsilicwu 25 canized rubbery article, the step which comprises g mace 25 adding 100 parts of a molten alloy of bis- Wood's Metal 0 0 50 muth, 25% lead, 12 /2% tin and 12 cadmium, s ifi Gravity at C 1 41 L46 and 4 Parts Of sulfur t0 1 0 parts Of a rubbery Tensls Elong.Shore 81530 sea: copolymer of 70 to 99 /270 of isobutylene and 30 g 1 2: V2? of iston'ietilie, thloroughly mixing the mol- 1 m .a Z n a 0:! 1n e ru bery copolymer by mas- 150mm- 307 55 tication at a temperature which is above the melting point of the alloy, and vulcanizing the TABLE V resulting composition at about 307 F. High density natural rubber RICHARD M. HOWLETT.

RAYMOND G. NEWBERG.

P tsb Ingredients flight REFERENCES CITED 5 k a h t 100 The following references are of record in the Si i file of this patent: lfiil'iiszaasiyitime35:12:32:::::: 1 UNITED STATES PATENTS glalifzgs (Tetra methyl thiuram disulfide) ;5 N b Name Date Celite (Hydrated amorphous silica) 25 ,2 KUZmlCk Oct. 14, 1941 Woods Metal 25 OTHER REFERENCES rmii filtiui ft o r 2 sp it? Enja B t 1 E c I (1948) s n Elongation-Shore at3osgc 690-38 T y u may Cure: able I.

min. at 287 F 2, 270-390 min. at 287 F 690- as 

1. IN THE METHOD OF PRODUCING A DENSE RUBBERY ARTICLE, THE IMPROVED STEP WHICH COMPRISES ADDING IN THE MOLTEN STATE FROM 1 TO 300 PARTS OF AN ALLOY OF 50% BISMUTH, 25% LEAD, 12 1/2% TIN AND 12 1/2% CADMIUM TO 100 PARTS OF A RUBBERY COPOLYMER OF 70 TO 99 1/2% OF ISBUTYLENE AND OF 30 TO 1/2% OF A CONJUGATED DIOLEFIN, THOROUGHLY MIXING THE MOLTEN ALLOY INTO THE RUBBERY COPOLYMER BY MASTICATION AT A TEMPERATURE WHICH IS ABOVE THE MELTING POINT OF THE ALLOY AND VULCANIZING THE RESULTING COMPOSITION AT A TEMPERATURE ABOVE THE MELTING POINT OF THE ALLOY. 